epidotide

Epidote is a group of sorosilicate minerals. The most common mineral in the epidote group is epidote itself, which has the chemical formula Ca2(Al,Fe)3(SiO4)3(SiO3)O(OH). It is a common rock-forming mineral found in a variety of metamorphic rocks. Epidote typically occurs in greenschist facies and amphibolite facies metamorphic rocks. It can also be found in altered igneous rocks and some hydrothermal veins.

The color of epidote ranges from green to greenish-black. The presence of iron influences the color, with higher iron content leading to darker shades. It has a vitreous luster and is often found in prismatic or acicular crystals, though it also occurs in massive or granular forms. Epidote has a Mohs hardness of 6 to 7, making it relatively hard. Its specific gravity is between 3.25 and 3.50. It exhibits piezoelectric properties.

Epidote is a characteristic mineral of regional metamorphism and is often used by geologists as an indicator of the metamorphic conditions under which a rock formed. It is not typically considered a gemstone due to its common occurrence and relatively low hardness, although some transparent, well-formed crystals may be used in mineral collections.